Mine roof supports usually employ a number of hydraulic telescopic props disposed between floor and roof engaging structures. To advance the supports behind a conveyor to follow up the winning progress, it is known to sub-divide the floor structure into a pair of skids or sills and to provide a hydraulic shifting ram between the sills. The ram is coupled to the sills on the one hand and to the conveyor on the other hand. By extending and retracting the ram and by bracing or relieving the props as appropriate the conveyor and the support can be advanced in stages towards the mineral face. It is known to link the shifting ram to resilient thrust rods which are guided on the sills to ensure the correct guidance. It is also known to provide a goaf shield between the roof engaging structure and the floor sills.
DE-OS No. 3700692 describes a known powered roof support in which the cylinder of the shifting ram is connected to a slidable guide engaging on guide rails on the floor sills and the piston rod is connected to a cross-piece which interconnects the front regions of the floor sills for relative vertical displacements. A thrust mechanism composed of a pair f resilient rods is coupled to the cylinder of the ram and serves for connection to the advance conveyor. A plate on the upper side of the rods near the front end regions of the floor sills serves to support hydraulic lifting units which serve to partly lift the sills during their advancement. This known support suffers from problems in that the thrust rod mechanism can tilt or position itself obliquely if the sills and the guide rails assume markedly different levels. In this case the guide can become jammed. Furthermore, since the guide is rigidly connected to the thrust rods these can cause the support plate to become inclined across the sills and the lifting units cannot then be supported properly.
DE-OS 3317801 describes another support in which the piston rod of the shifting ram is connected via a guide rod to an advance abutment, i.e. a conveyor. A frame around the ram is connected to the cylinder of the ram and is linked via a joint to a cross-piece connected between the floor sills. A pair of parallel guide rods lie between the frame and are guided in openings in the frame. This guidance system also has certain disadvantages.
An object of the invention is to provide an improved form of advanceable roof support.